This invention relates generally to passenger vehicle inflatable restraints and, more particularly, to an inflatable restraint system including means for augmenting gas delivered from an inflator to an air bag.
Many passenger vehicles manufactured today are equipped with supplemental inflatable restraints for the vehicle driver, commonly known as air bags. An increasing number of vehicles are being equipped with air bags for the front seat passenger. This air bag is part of an air bag assembly which includes an inflator attached to the air bag and a reaction canister housing the inflator. The air bag is mounted on the canister above the inflator.
This air bag assembly is located in a recess in the vehicle instrument panel for deployment of the air bag through an instrument panel opening which is normally closed by a cover door. The inflator is actuated by a signal received from a vehicle deceleration sensor to discharge pressure gas through discharge ports into the air bag interior. Upon inflation, the air bag forces the cover door Open and deploys into the passenger compartment rearwardly of the instrument panel.
Inflators utilized in this type of installation generally have a cylindrical outer casing. The reaction canister has a U-shaped bottom portion, comprising part-cylindrical bottom and side walls which house the inflator. The canister has a top opening that connects to the air bag interior.
Various types of cylindrical inflators are used in this arrangement. In one, the canister is mounted on the bottom wall and gas discharge ports are located on only the side of the inflator facing the air bag opening. This is known as a directed thrust inflator and is characterized by having a downward resultant reaction force when actuated. It also produces an area of reduced pressure between the sides and bottom of the inflator and canister upon actuation because of the directed thrust.
Because air bags are utilized to give protection to occupants in the event of sudden vehicle deceleration, the air bags must deploy quickly. This requires that the inflator generate great quantities of pressure gas and deliver it to the air bag immediately upon actuation to enable deployment of a properly pressurized air bag within a predetermined short time span.
Another type of inflator has been developed, which features gas discharge ports located on all, or at least diametrically-opposite sides of the casing. This arrangement of the discharge ports makes the inflator thrust neutral, since the gas discharge forces on opposite sides of the inflator cancel, with no resultant forces. This type of inflator is usually end mounted to the end walls of a reaction canister having a U-shaped cross section with a rectangular top opening. The inflator is mounted in spaced relation to the bottom and side walls which direct all gas discharged upwardly through the canister top opening into the air bag. Upon actuation, there is no reduced pressure area between inflator and canister, since gas is discharged from both sides of the inflator.
An inflator arrangement for increasing gas output is illustrated in U.S. Pat. No. 4,846,368--Goetz in which a directed thrust inflator is used in a reaction canister having holes in its side walls. These holes are normally covered by flexible flaps. Upon actuation of the inflator, the discharge of pressure gas from the canister causes a pressure reduction around the sides of the canister, due to the Bernoulli effect. This resultant pressure imbalance forces the flaps inwardly to aspirate ambient air to the canister. This supplemental ambient air augments the gas discharged by the inflator, increasing the total gas volume available to inflate the deploying air bag. Should pressure rise above a desired level in the Goetz arrangement, these flexible flaps will close. Auxiliary rear vent holes are provided.
A similar arrangement is shown in U.S. Pat. No. 4,928,991--Thorn which also utilizes directed thrust gas generation and side wall aspiration holes covered by a flap. In both of these patents, an increase in air bag pressure causes the flaps to close. This requires other means of accommodating pressure increases. Also, the use of directional gas generators produces a reaction force on the inflator, requiring a rugged mounting arrangement.
The mere substitution of a thrust neutral, non-directional inflator in the Goetz and Thorn devices would not function the same, since the necessary area of reduced pressure would not exist and the flaps would not open.
It would be desirable to provide a simplified air bag installation which uses a thrust neutral inflator that enables the augmentation of discharge gas with ambient air.
It would also be desirable to provide such an installation which provides relief for excessive air bag pressure.